Onan Generator: “Fault 13”
warning RV generator fault codes
What it means
Undervoltage fault. The controller could not hold the generator's AC output at rated voltage — usually because the connected electrical load is dragging the output down.
Most likely causes
- Too many appliances drawing at once (air conditioners plus active battery/inverter chargers) most likely
- High-draw charger running as a hidden load while other loads are on common
- Internal voltage-regulation or winding fault less common
Safe checks you can do yourself
- Turn off some appliances — especially air conditioners and any battery/inverter charger — and restart.
- Lower the battery charge rate on your inverter/charger if it is pulling a large 'invisible' load.
- Verify the total connected wattage is within the generator's rating.
How to reset / clear Fault 13
- Reduce the load, then restart the generator from the control switch.
- If it runs and holds voltage with fewer loads, add loads back gradually.
When to call a technician
If undervoltage persists with only a modest load connected — that points to a regulator or generator-end fault needing a dealer.
Applies to
Marquis Gold · QG 4000 · QG 5500 · KY series · HGJAA · HGJAB · HGJAC · HGJAD · HGJAE · HGJAF
FAQ
What does Onan Generator code "Fault 13" mean?
Undervoltage fault. The controller could not hold the generator's AC output at rated voltage — usually because the connected electrical load is dragging the output down.
How do I reset Onan Generator Fault 13?
Reduce the load, then restart the generator from the control switch. If it runs and holds voltage with fewer loads, add loads back gradually.
What is the most common cause of Fault 13 on a Onan Generator?
The most likely cause is too many appliances drawing at once (air conditioners plus active battery/inverter chargers).
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Sources
- Onan Troubleshooting Codes (Service Manual Table 5) — Undervoltage Fault — Code No. 13 (Cummins Onan (hosted by Heartland Owners))
Note: Code 13 is read out as a second-level code after Code 3 flashes.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.